Dispersion of terephthalic acid in detergent containing hydrocarbon oil medium

ABSTRACT

TEREPHTHALIC ACID IS DISPERSED IN A HYDROCARBON MEDIUM CONTAINING HIGHLY HINDERED ACYLATE ALKYLENE POLYAMINES.

United States Patent O answer on THE DISCLOSURE Ter ephthalic acid is dispersed in a hydrocarbon medium containing highly hindered acylated alkylene polyamines.

BACKGROUND OF THE INVENTION Field of the invention A common corrosion inhibitor employed in lubricating oils is terephthalic acid or its lower alkyl derivatives. Terephthalic acid is insoluble in a hydrocarbon medium. Therefore, a basic or other type of oil solubilizing material is used in order to introduce the terephthalic acid into the hydrocarbon medium and prevent its settling out.

Terephthalic acid has found particular use with ashless detergents. These detergents are prepared, for the most part, from an oil soluble acylating agent and an alkylene polyamine. With acylated polyamines having at least 3 amino nitrogens and only one solubilizing acid group, terephthalic acid is readily dispersed by means of the ashless detergent. However, it is found that with two oil soluble acylating groups on an alkylene polyamine, even one having as many as amino nitrogens, the terephthalic acid is not readily dispersed in the hydrocarbon medium at the desired concentrations. Therefore, alternative ways have had to be found to stably disperse the terephthalic acid at desired concentrations in a hydrocarbon medium containing a dior higher acylated alkylene polyamine.

Description of the prior art US. Pat No. 2,900,339 discloses the use of tertiary hydrocarbon amines to disperse terephthalic acid in a mineral lubricating oil containing calcium petroleum sulfonate.

U.S. Pat. No. 3,287,271 teaches dispersing aromatictype dibasic acids with succinimide ashless detergents, having about a 1:1 mole ratio of alkenyl succinic group to alkylene polyamine, by heating the acid with the ashless detergent in a hydrocarbon medium.

US. Pat. No. 2,809,160 teaches the use of aromatic dibasic acids as corrosion inhibitors in lubricating oils.

Copending application Ser. No. 684,922, filed Nov. 22, 1967, now US. 3,538,000, teaches the use of the silyl esters of terephthalic acid to provide corrosion inhibition in combination with an ashless detergent having about 2 alkenyl succinic anhydride groups per alkylene polyamine group.

SUMMARY OF THE INVENTION Terephthalic acid or its lower alkyl derivatives are stably dispersed in a hydrocarbon medium having from 3 to 60 weight percent of a highly hindered basic amine containing ashless detergent. The terephthalic acid is dissolved in an auxiliary solventa tertiary alkanol of from 4 to 8 carbon atoms or dimethyl sulfoxide (DMSO), the solution mixed with a hydrocarbon oil solution of the ashless detergent and the auxiliary solvent separated by vaporization or other convenient means. The terephthalic acid is introduced in at least 1 weight percent based on the ashless detergent present in the oil.

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DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of this invention comprises dissolving the terephthalic acid or its derivative in an auxiliary solventa tertiary alkanol of from 4 to 8 carbon atoms or DMSO combining the terephthalic acid solution with a hydrocarbon solution of the hindered acylated amine ashless detergent and then separating the auxiliary solvent.

Depending on the terephthalic acid and auxiliary solvent used, the concentration of terephthalic acid in the solvent will generally be in the range of about 0.05 to 5 weight percent, more usually about 0.1 to 2 weight per? cent. The temperature of the auxiliary solvent will vary from about 20 C. to about 200 C., more usually in the range of about 20 C. to 150 C. With the alkanols, the temperature will be in the range of 50 C. to about 150 C.

The ashless detergent solution will generally have from about 3 to 60 weight percent, more usually from about 10 to 55 weight percent of the ashless detergent, The terephthalic acid solution may be added to the oil solution or the oil solution to the terephthalic acid solution. With the alkanols, it is frequently convenient to have the terephthalic acid solution refluxing and add the oil solution at ambient temperatures to the refluxing tere hthalic acid solution. The order or method of addition is not critical to this invention. The conditions should be such, however, that the terephthalic acid does not precipitate out to any significant degree upon combining the two solutions.

It is frequently convenient to dilute the hydrocarbon solution with the auxiliary solvent, particularly the tertiary alkanol, prior to addition of the terephthalic acid solution. Ordinarily, the oil solution will be diluted with from about 0.1 to 2 parts of the auxiliary solvent, particularly, alkanol, per part of hydrocarbon oil solution. Alternatively, the oil solution may be diluted with volatile hydrocarbons (610 carbon atoms) in about from 0.5 to 5 parts per part of oil solution.

The solutions are then mixed at ambient (20 C.) or elevated temperatures. With the alkanols, the solutions will usually be mixed at elevated temperatures, generally from about 50 to 290 C., more usually from about to 150 C. After suflicient time has evolved so that the solution appears clear, the auxiliary solvent may be removed by vaporization or other convenient means, e.g., centrifugation. The auxiliary solvent may be distilled off, stripped in vacuum, or removed by any other convenient means which efficiently and rapidly removes the auxiliary solvent from the hydrocarbon solution.

The preferred corrosion inhibitor will ordinarily be terephthalic acid, although this invention may also be used with lower alkyl substituted terephthalic acids, wherein the alkyl group is of from 1 to 4 carbon atoms. Illustrative substituted terephthalic acids are 2-methyl terephthalic acid, 2-tert.-butyl terephthalic acid, 2-isopropyl terephthalic acid, etc.

The tertiary alkanols which find use will be alkanols of from 4 to 8 carbon atoms, preferably tert.-butyl alcohol. Other alkanols include tert.-amyl alcohol, 2- methyl-Z-heptanol, 3-methyl-3-hexanol, etc.

The hydrocarbon solution will generally have as the medium, a hydrocarbon oil of lubricating viscosity. These lubricating oils may be naturally derived from petroleum oils, such as paraffin base, naphthenic base, asphaltic base, and mixed base lubricating oils. Usually, the oils will be substantially parafiinic or naphthenic having less than about 20 weight percent aromatics. Lubricating oils generally have viscosities of from about 35 to 50,000 Saybolt Universal Seconds (SUS) at F. The oils generally have boiling points of from about to 500 C.

The ashless detergents are those combining an alkylene polyamine having from 3 to 6 nitrogen atoms, and alkylene groups of from 2 to 6 carbon atoms, with at least 1.8 moles of an alkenyl succinic acid per mole of alkylene polyamine. The product of the reaction may be a succinamic acid, a di-succinamide, or succinimide, or most likely combinations thereof.

These compositions are prepared by heating about 1.8 to 3 moles of an alkenyl succinic anhydride, usually a polyisobutenyl succinic anhydride, having a molecular weight in the range of from about 500 to 2,000 with an alkylene polyamine, usually an ethylene polyamine or propylene polyamine, having from 3 to 6 amine nitrogen atoms, at a temperature in the range of 85 C. to 200 C. for a time suflicient to effect reaction. Any water formed during the reaction is driven otf.

These detergents are described in US. Pat. Nos. 3,219,666 and 3,172,892, the disclosures of which are incorporated herein by reference.

Of particular interest are the polyisobutenyl succinimides or analogous acyl amine derivatives of triethylene tetra-amine and tetraethylene pentamine, wherein the polyisobutenyl groups are of from about 700 to 1,500 molecular weight and the mole ratio of polyisobutenyl succinic anhydrides to alkylene polyamine is in the range of 1.8 to 2.221.

The oil solutions containing the anhydride alkylene polyamine reaction products will usually have alkalinity values in the range of 15 to 50.

The final product will have at least one weight percent of the terephthalic acid or derivatives based on the ashless detergent, and more usually from about 1.5 to weight percent, preferably 1.5 to 3.5 weight percent.

Examples The following examples are offered by way of illustration and not by Way of limitation.

Example I.-A 46 weight percent solution of the reaction product of 2 moles of polyisobutenyl succinic anhydride (polyisobutenyl of about 1,000 average molecular weight) and tetraethylene pentamine in 480 neutral oil (98.6 g. of reaction product in solution) was diluted with 100 m1. of tert.-butyl alcohol and the solution added to a refluxing solution of 1.4 g. of terephthalic acid in 600 ml. of tert.-butyl alcohol. The reaction became cloudy. After 90 hrs. of stirring at reflux, the insoluble cloud had settled on the sides of the flask. The clear solution was stripped in vacuo yielding a solution having 1.4 weight percent terephthalic acid. The product was filtered through Celite. Titration determined the amount of terephthalic acid incorporated was 1.4 weight percent.

Example II.The reaction product described in Example I as an oil solution (98.6 g.) was diluted with 300 ml. of hexane and a solution of 6.3 g. of terephthalic acid in dimethyl sulfoxide was added and the mixture stirred at room temperature for 20 hrs. The mixture was centrifuged and the hexane layer stripped. The DMSO layer was isolated and analyzed, showing that the oil solution had 0.81 weight percent terephthalic acid. The oil solution was titrated, the acid number indicating 0.82 Weight percent of TPA being present.

If terephthalic acid is added to the same oil solution used in Example I, by the prior art method of heating, the maximum amount of terephthalic acid which can be incorporated into the oil solution is about 0.3 weight percent.

The oil solution containing the terephthalic acid was found to be bright and after one week of storage at 150 F., there was no noticeable loss from the solution of the terephthalic acid.

TABLE I Percent Bearing viscosity Terephthalio acid, Test, weight. increase, wt. percent hrs. loss, rug. 100 F., SUS

40 141 7. 5 422 10. 0 0.03... 40 30 80 4. 9 0.1 4U 26 4. 8 so 47 5. 8

It is evident from the above results by employing the process of this invention, terephthalic acid can be introduced into lubricating oils containing highly hindered amine nitrogen-containing acylated detergents in an amount sufiicient to provide eifective corrosion protection.

I claim:

1. A method for introducing terephthalic acid or mono (lower alkyl) substituted terephthalic acid into a hydrocarbon oil medium containing from 3 to 60 weight percent based on the total composition of the reaction product of alkenyl succinic anhydride, having a molecular weight in the range of 500 to 2,000, and an alkylene polyamine having from 3 to 6 amine nitrogen atoms and alkylene groups of from 2 to 6 carbon atoms, wherein the mole ratio of anhydride to alkylene polyamine is at least 1.8:1; which comprises dissolving said terephthalic acid or mono (lower alkyl) substituted terephthalic acid in an auxiliary solvent, which is a tertiary alkanol of from 4 to 8 carbon atoms or dimethyl sulfoxide, combining with agitation the terephthalic acid solution with the hydrocarbon oil solution and removing the auxiliary solvent, said terephthalic acid or mono(lower alkyl) substituted terephthalic acid being present in an amount of from 1.0 to 5.0 weight percent based on the said reaction product.

2. A method according to claim 1, wherein said auxiliary solvent is said tertiary alkanol and wherein the combining is carried out at an elevated temperature in the range of 50 to 290 C.

3. A method according to claim 1, wherein said tertiary alkanol is tert.-butanol and the acid is terephthalic acid.

4. A method according to claim 1, wherein dimethyl sulfoxide is the auxiliary solvent and the combining is carried out at room temperature.

References Cited UNITED STATES PATENTS 2,809,160 10/1957 Stewart et a1. 25257 X 3,245,909 4/1966 Lowe 25251.5 A 3,287,271 11/1966 Stuart et a1 25251.5 A

DANIEL E. WYMAN, Primary Examiner W. I SHINE, Assistant Examiner US. Cl. X.R. 25257, 396 

